1. Field of the Invention
The present invention relates to a vibration damping tool that is able to suppress vibration generated during a process to machine cut a material.
2. Description of the Related Art
Conventionally, a head portion on which inserts are mounted is attached to a tool body, for example, such as an arbor. A material to be cut may be cut by moving the tool body forward while rotating it around an axis. Alternatively, an insert may be attached to the distal end of a tool body such as a boring bar and the material to be cut may be cut as it is rotated around an axis.
At this time, the base end of the tool body is supported in a cantilever manner by a gripping portion of a machine tool and when a cutting processing is performed on the material to be cut using the cutting edge of an insert, resonance is created from the natural vibration of the tool that derives from the projecting length of the tool from the gripping portion to the blade and the like and vibration that acts on the tool as a result of cutting force and the like, and cutting edge vibration is thereby generated. This chatter vibration worsens as the ratio L/D, which is the length L that the tool body projects outwards relative to the diameter D of the tool body, increases, leading to a deterioration in the surface roughness of the processed surface of the material being cut, or in severe cases, may lead to a breakage of the tool body itself. Therefore, an upper limit value of approximately 3 to 4 is set for the ratio L/D, which has created problems particularly when an increase in the ratio L/D is desired such as, for example, in deep groove processing of a metal die or in boring processing using a boring bar.
In order to solve the above described problem, as is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 11-19839, for example, the material used for the tool body may be formed from a material having a high Young's modulus. Alternatively, as is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 9-94706, a cemented carbide member may be fixed to the outer peripheral portion of the tool body along an axial direction thereof by brazing.
In tools such as these, by increasing the rigidity of the tool body, the aim is to raise the undamped natural frequency of the tool body and thereby make it difficult for resonance to be generated. However, because chatter vibration increases as the ratio L/D increases, a fundamental solution has hitherto not been possible.
As another means of solving this problem, as is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 59-1106, for example, a hollow portion is formed inside the tool body and a weight member, which is elastically supported by two elastic members forming a ring shape, is housed in this hollow portion. In addition, a viscous fluid such as silicone oil is sealed in the hollow portion so as to fill the gap between the weight member and the inner wall surface of the hollow portion.
FIG. 10 shows an example in which this type of structure is used in a rotation cutting tool. Chatter vibration generated in the tool body 100 excites vibration in a weight member 102 that is elastically supported by elastic members 101 and 101. Subsequently, the vibration of the weight member 102 is damped by being transmitted to viscous fluid 103 that fills the area around the weight member 102. As a result, chatter vibration of the tool body 100 is suppressed. Namely, this tool body 100 is provided with a dynamic vibration absorber made up from a weight member 102 forming a mass element, elastic members 101 and 101 forming spring elements, and viscous fluid 103 forming a damping element. Accordingly, vibration of the tool body 100 is damped and absorbed by the dynamic vibration absorber.
However, the viscous fluid 103 that is used as a damping element in the dynamic vibration absorber has a drawback in that it is easily affected by heat so that the viscosity thereof changes. When heat that is generated during cutting is transmitted to the viscous fluid 103 and the temperature of the viscous fluid 103 itself increases, the viscosity deteriorates and the damping affect also deteriorates causing concern that chatter vibration will not be able to be suppressed.
Moreover, a sealed structure is needed in order to ensure that the viscous fluid is sealed inside the tool body and does not leak out, which necessarily entails a complicated structure for the tool body 100.
Furthermore, because a structure is employed in which the weight member 102 is supported by the elastic members 101 and 101, when a tool body 100 that is provided with this type of dynamic vibration absorber is used as a rotation cutting tool, because eccentricity is generated in the weight member 102 as a result of the rotation of the tool body 100, problems such as it becoming necessary to lower the rotation speed occur which mean that this structure is not suitable for use as a rotation cutting tool.